Air Pollution

 

AIR POLLUTION

Air pollution refers to the undesirable change inn the quality of air due to contamination of chemical and particulate matter or biological agents.

 

HISTORY OF AIR POLLUTION

·       The origin of air pollution on the earth can be traced back to the time when man started using firewood for cooking and heating.

·       It was noticed as a problem 700 years ago in London in the form of smoke pollution.  The major disaster ‘London smog’ occurred in 1952 caused more than 4000 deaths due to accumulation air pollution over the city for five days.

·       The severe air quality problems due to petrochemical smoke from vehicles were observed for the first time in los angels.

·       The air pollution control act in India was passed in 1981.

·       The greatest industrial disaster took place in Bhopal on the night of 2^nd December, 1984 due to the leakage of poisonous methyl isocyanate gas from the union carbide company.  It caused the death of 3000 of human beings.

 

THE ATMOSPHERE:

Composition of the air:  The atmosphere is made up of a mixture of gases.  Normally the air consists of 78.08% if nitrogen, 20.95% oxygen and 0.93% argon.  Other gases like carbon dioxide, hydrogen, neon, helium, methane and ozone are also present in very small quantities.

 

Structure of atmosphere:  The atmosphere is divided into four different layers.

1)  Trophosphere:  It is the lower most layer.  It extends 18km above the sea level at the equator.  It contains 75% of the mass of the earth’s air.  Temperature decreases with height in this layer.

 

2)  Stratosphere:  It is the second layer of the atmosphere.  It extends to a height of 48km above the sea level.  The volume of water vapour here is about 1000 times less, while the volume of ozone is about 1000 times greater.  The presence of ozone in the stratosphere prevents about 99% of the sun’s harmful ultra radiation reaching the earth.  Hence, it protects human from cancer and damage to immune system.  It provides flying conditions for jet air crafts.

 

3)  Mesosphere:  It extends to height of 82km above the sea level temperatue of this layer decreases with increasing height, reaching upto -110*c at the top.

4)  Thermosphere:  It extends to a height of 82 to 400 km.  This layer contains electrically charged particles called ions.  Hence, this layer is also called as Ionosphere.  Temperature starts increasing with height in the layer because of radiation from the sun.

 

AIR POLLUTANTS

Air pollutants are directly emitted from identifiable sources.  They are produced both by natural events and human activities.  These are called Primary pollutants.  They are five primary pollutants that together contribyte to about 90% of global air pollution.  These are carbon oxides, nitrogen oxides, sulfur oxides, volatile organic compounds and suspended particulate matter.

Carbon Monoxide is a colorless, odorless and toxic gas produced from the incomplete burning gas, coal or wood.  Vehicular exhausts are the single largest source of carbon monoxide.

Sulphur oxides are produced when sulfur containing fossil fuels are burnt

Nitrogen oxides are found in vehicular exhausts.

Hydrocarbons are group of compounds consisting of carbon and hydrogen atoms.  They are washed out of the air when it rains.

Particulates are small pieces of solid materials.

The following are the different types of particulates.

1.  Aerosol: It is a general term for particles in air.

2.  Mist:  Aerosal consisting of liquid droplets.

3.  Dust:  Aerosal consisting of solid particles.

4. Smoke:  Aerosal consisting of mixture of solid and liquid particles produced by chemical reaction.

5.  Fume: It is similar to smoke but produced from condensation of hot vapors of metals

6.  Fog:  Aerosal constisting of water droplets

7.  Smog:  Term used to describe a mixture of smoke and fog

 

The primary pollutants by chemical reaction produce secondary pollutants.

Lead is major air pollutant emitted by vehicles.  The use of unleaded petrol is one way of reducing this pollutant.

EFFECTS OF AIR POLLUTION ON HUMAN HEALTH

Continuous smoking or exposure to air pollutants can cause lung cancer, asthma, chronic bronchitis and pulmonary edema

1.  Carbon monoxide:  Cigarette smoking is responsible for the greatest exposure to carbon monoxide. Exposure to air containing even 0.001% carbon monoxide for several hours can cause coma and death.  It also reduces the oxygen carrying capacity of hemoglobin in the blood which leads to headaches, drowsiness, nausea and blurred vision.

2.  Sulfur dioxide:  produces irritation of the respiratory tissues and in long term exposure causes bronchitis and lung cancer.

3.  Nitrogen oxides:  Affect the respiratory tract leading to bronchitis and asthma.  Particles from asbestos, ash can cause cancer in lungs

5.  Volatile compounds:  Benzene and formaldehyde and toxic particulates can cause mutation, reproductive problems and cancer.  Repeated inhalation of ozone can cause coughing chest pain, breathlessness and irritation eyes, nose, and throat.

 

EFFECTS OF PLANTS

Long term exposure of plants to air pollutants cause the following effects

1.  Disappearance of chlorophyll by sulphur di oxide affects photosysthesis

2.  Less carbohydrate production

3.  Damage of leaf tissue, buds, flowers and fruits

4.  Reduction in growth rate or suppression of growth

5.  Increases possibility to disease and pest attack

6.  Decrease in crop yield, smaller fruits and less nutritious products

7.  Leaves turn to yellow, brown

 

EFFECTS ON MATERIALS

The air pollutants can also break down the exterior paint on cars and houses.  All over the world,  air pollutants have discolored irresplaceable effects to monuments, historic buildings, marble statues and natural beauty sites

 

EFFECTS ON THE STRATOSPHERE

The upper stratosphere consists of ozone which acts as an effective screen for uv light.  Ozone is a form of ozygen with three atoms instead of two.  The small changes in ozone oncentration produce drastic effects on the life on earth.  The accumulation of air pollutants can accelerate the breakdown of ozone.  In 1985, large scale destruction of ozone called ‘ozone hole’ was created by chlorfluro carbons.

Chlorofluoro carbons causes depletion of ozone.  They are stable, non flammable, nontoxic and harmless to handle.  But they are used in air conditioners, refrigerators and fire extinguishers.

Halons are similar in structure to CFC’s but contain bromine instead of chlorine.  They are most dangerous than CFC ad used as fire extinguishing agents.  Ozone depletion is prevailing in south poles due to extreme ice crystals.

Effects of ozone depletion

1) Depletion on human health:

Sunburn, cataracts, aging of the skin, skin cancer are caused by uv radiation.  It weakens the immune system which leads to measles, chickenpox and other viral diseases.

2) Zoophanktons:

They are damaged by UV radiation.  In zooplankton the breeding period is shortened.  Changes in total number and species compositon disrucpt the food fish production.

3) Food production:

The UV radiations affects photosynthsis, reduces and nutrient content and decreases the growth in legumes and cabbage.

4) Materials:

Increased UV radiation damages paints and fabrics leading them to fade faster

5) Effect on climate:

Global warming a phenomenon by which earth is warming up due to the increased concentration of certain gases like nitrogen oxides, carbon di oxide, methane and CFCs.  They absorb the heat in the form of infra red radiation near the earth’s surface as in a glass green house which allows solar radiation to enter which is absorbed by the objects inside.  Hence, this is known as “Green house effect”.

There could be several adverse effects of global warming

1.  With a warmer earth, the polar ice caps will melt causing rise in sea level and flooding of coastal area.

2.  If sea level rises by 3 metres, the Maldives will disappear completely beneath the waves

3.  Rise in temperature will affect agricultural production

4.  Temperature rise by global warming also affects changes in species of plants, insects, live stock and microorganisms.

AIR POLLUTION IN INDIA

The world health organization rater new delhi as the fourth 4^th most polluted city In the world.  According to central pollution control board (2003), Ahmedabod’s air is the most noxious followed by Kanpur, shalapur and lucknow.  Nitrogen dioxide level increases in Kolkata and delhi due to heavy vehicular traffic and density.  Implementation of compressed natural gas program has improved the quality of air.

Marble cancer to Taj mahal:  Increased level to sulfur dioxide and suspended particulate matter caused a fungal growth that corroded the surface to taj mahal giving a yellow tinge called ‘ Marble cancer’.  The supreme court of India ordered 292 industries in the vicinity to either adopt pollution control measures or shut down.

CONTROL OF AIR POLLUTION

1.  The emission of exhaust from automobiles can be reduced by devices such as ventilation valve and catalytic converter

2.  Electrostatic precipitators can reduce the smoke and dust from industries.

3.  Certain gases can be removed by filtration or absorption through activated carbon

4.  Greater emphasis should be given on the pollution prevention rather than control

5.  The quality of vehicular fuel should be improved

6.  At the Government level pollution can be controlled by farming legislations